Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by bradykinesia, rigidity, resting tremor, and ataxia. These symptoms are caused by decreased dopamine release in the striatum. Clinically, PD is defined by presence of Lewy bodies, intracellular neuronal inclusions in the substantia nigra and at other sites in the brain. Estimated prevalence of this disease is 100 to 200 per 100,000 population including males and females across the entire age group. Current treatment for PD comprises dopaminergic medications that include levodopa, dopamine agonists (DAs), monoamine oxidase-B (MAO-B) inhibitors. FIG. 1 provides few examples of pharmaceutically important benzyloxy-benzylamine derivatives. Many of these benzyloxy-benzylamines with various amine functions were studied and has been patented as sodium channel blockers. Among them, safinamide ((S)-N2-{4-[3-fluorobenzyl)oxy]benzyl}-alaninamide methanesulfonate) is a noted example which is under phase III clinical trials for treatment of Parkinson's disease. Its mechanism of action is manifold which comprise MAO-B and dopamine uptake inhibition. Further, safinamide is believed to block voltage-dependent sodium channels, modulates calcium channels and reduction of glutamate release in the central nervous system.
WO1998003472 discloses serinamide, glycinamide, alaninamide and phenylalaninamide derivatives of a compound (I). These compounds (I) are useful for the treatment of neurological diseases.
EP2474521 discloses high purity degree (S)-2-[4-(3-fluorobenzyloxy)-benzylamino]propanamide (safinamide) or (S)-2-[4-(2-fluorobenzyloxy)-benzylamino]propanamide (ralfinamide) or a salt thereof with a pharmaceutically acceptable acid with a content of the respective impurity (S)-2-[3-(3-fluorobenzyl)-4-(3-fluorobenzyloxy)-benzylamino]propanamide or (S)-2-[3-(2-fluorobenzyl)-4-(2-fluorobenzyloxy)-benzylamino]propanamide.
US2009149544 relates to novel alpha-aminoamide derivatives, their pharmaceutically acceptable salts, solvates, and hydrates thereof. The application also provides compositions comprising a compound and the use of such compositions in methods of treating diseases and conditions that are beneficially treated by administering an inhibitor of monoamine oxidase type B (MAO-B) and/or a sodium (Na.sup.+) channel blocker, and/or a calcium (Ca.sup.2+) channel modulator.
The strategy employed in the art to prepare benzyloxy-benzylamine derivatives including safinamide or its analogue ralfinamide is chiral pool approach starting from L-alaninamide and reductively aminating with 4-(3-fluorobenzyloxy)benzaldehyde. Although this method is very simple and straightforward, it suffers from several serious drawbacks, such as need to use toxic reagents such as sodium cyanoborohydride and further formation of toxic by-products such as hydrogen cyanide and sodium cyanide and other toxic impurities in large-scale production Importantly, the possibility of generating a range of safinamide analogues by means of the chiral-pool approach is limited in terms of the structure and stereochemistry of the products because of inadequacies in the availability of D-alaninamide and its analogues
Hence, the developments of newer methods for the preparation of compounds of formula (I) comprising safinamide and related analogues are highly desirable.